Study Connects Heat, Physical Exertion with Firefighter Heart Attacks

Heart illustration with artery close up. (copyright American Heart Association)
Exposure to extreme heat and physical exertion during firefighting may trigger the formation of blood clots and impair blood vessel function, changes associated with increased risk of heart attack, according to new research in the American Heart Association’s journal Circulation.

Cardiovascular events are the leading cause of death among firefighters and are responsible for roughly 45 percent of on-duty firefighter fatalities annually in the United States.

“These harsh conditions can cause injury to the heart muscle in healthy firefighters and may explain the link between fire suppression and risk of heart attacks,” said Nicholas Mills, M.D., Ph.D., lead researcher and chair of cardiology and consultant cardiologist at the University of Edinburgh in Scotland.

Heart rate and blood pressure were monitored for 30 minutes before the exercises and for 24 hours following.

“The firefighters wore heart monitors that continuously assessed their heart rate, heart rhythm and the strength and timing of electrical impulses passing through each part of the heart. We analyzed these to look for evidence of heart strain that might signify a lack of blood being delivered to the heart muscle,” Mills said.

The findings uncovered processes known to be key in triggering heart attacks in people at risk.

“We assessed blood clotting in response to both extreme heat and physical exertion. In this setting an increase in blood clotting is likely an exaggerated normal physiological reaction to both these stressors,” Mills said.

“Lower blood pressure immediately following fire suppression is likely due to dehydration and an increase in blood being diverted to the skin to help the body cool down. We discovered the core body temperature increased, on average, nearly 2 degrees Fahrenheit over 20 minutes. And increases in hemoglobin occur as the body loses water and the blood gets more concentrated,” Mills said.

Researchers said their study suggests anyone who is exercising in extremely high temperatures should keep well hydrated and allow time to cool down afterward.

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